This invention relates to a process for producing an unsaturated polyester from polyethylene terephthalate (hereinafter abbreviated as PET), particularly waste (or scrap) PET, and an unsaturated polyester resin composition and a molding compound comprising the resulting unsaturated polyester.
It is known that waste PET, whether post-consumer or non-post-consumer, can be recycled by depolymerization in a glycol, followed by reaction with an unsaturated polybasic acid and a glycol to produce an unsaturated polyester. This technique has recently been re-studied as disclosed in JP-A-11-60707, JP-A-8-151438, and JP-A-11-181067.
However, the unsaturated polyester obtained from waste PET has poor compatibility with unsaturated monomers such as styrene, and its solution has poor solubility stability with time. This seems attributable to the crystallinity originated in the PET segments and the intermolecular hydrogen bond strength of the ester moiety between ethylene glycol originated in PET and fumaric acid. A combined use of various glycols has been a generally followed practice to improve the compatibility as taught in JP-A-8-151438. The chief aim of the combined use of a plurality of glycols is improvement on compatibility with unsaturated monomers such as styrene. Studies taking into consideration the quality or performance of molded articles obtained from the resulting resin composition have not been made to date.
Sheet molding compounds (SMC), bulk molding compounds (BMC), etc. comprising the unsaturated polyester should contain a thermoplastic resin as a low profile additive. A polystyrene resin is of frequent use as a low profile additive for its water resistance and inexpensiveness. As stated above, the conventional unsaturated polyester prepared from waste PET has poor compatibility with the low profile additive or poor uniformity retention in a mixed state with the low profile additive so that they are liable to separate from each other during a thickening step or storage of molding compounds comprising the unsaturated polyester. Molded articles obtained from such a molding material are inferior in appearance and quality to those obtained from a molding material comprising an ordinarily produced unsaturated polyester.
An object of the present invention is to eliminate the drawbacks of molded articles of a polyester resin composition obtained from PET, i.e., to improve compatibility of the polyester resin with a low profile additive and to improve appearance and quality of the molded article.
In order to increase usefulness of the unsaturated polyester prepared out of PET, the present inventors have conducted extensive investigation and reached the present invention as a result.
The present invention provides a process for producing an unsaturated polyester comprising the steps of
(1) (A) depolymerizing polyethylene terephthalate with a polyhydric alcohol, (B) adding maleic anhydride to the depolymerization product to allow them to react with each other, and (C) adding dicyclopentadiene to a carboxyl group derived from the maleic anhydride to cause addition reaction and
(2) adding a polyhydric alcohol and/or a polybasic acid to the reaction product obtained in step (1) to cause polycondensation reaction.
Further, in the above process of the present invention, if strict control of the addition rate of the dicyclopentadiene to the carboxylic group of the maleic anhydride in step (C) is carried out, an unsaturated polyester having very stable quality can be obtained.
The invention further provides an unsaturated polyester resin composition comprising the unsaturated polyester obtained by the above process and a polymerizable unsaturated monomer.
The invention furthermore provides a molding compound comprising the unsaturated polyester resin composition.
The PET which can be used as a starting material in step (A) is a polymer synthesized essentially from terephthalic acid and ethylene glycol and includes the waste generated in PET production, recycled PET of various waste PET molded articles, and regrinds of waste PET generated in production of PET molded articles. Typical are regrinds, called waste PET or regenerated polyester, obtained by physically and mechanically grinding PET bottles into chips, powder, pellets or flakes, which preferably have an average particle size of 1 to 10 mm.
The term xe2x80x9cpolyethylene terephthalate (PET)xe2x80x9d as used herein includes not only polymers consisting of terephthalic acid and ethylene glycol but those further comprising other units of cyclohexanedimethanol, isophthalic acid, naphthalenedicarboxylic acid, etc. as a modifying comonomer.
PET does not always need to be transparent. Colored (e.g., green-colored) or printed PET is also useful unless the resulting molding article is not limited in hue, etc.
The maleic anhydride which can be added in step (B) is a compound obtained by heat dehydration of maleic acid or catalytic oxidation of benzene with air. Commercially available maleic anhydride, preferably of such a grade as has a purity of 95% or more and high resistance to thermal coloration can be used.
The dicyclopentadiene (hereinafter abbreviated as DCPD) which can be used in step (C) does not need to have high purity, and commercially available products can be employed. It is preferred to use DCPD which is composed of components that do not form a large amount of gel (heat crosslinking product) during polycondensation and has a purity of 85% or higher.
The polyhydric alcohol with which PET is depolymerized in step (A) is not particularly limited and is appropriately selected according to the purpose. It is desirable to use such a polyhydric alcohol as depolymerizes PET when added in a small amount and completes the depolymerization smoothly and rapidly at a relatively low temperature of 260xc2x0 C. or lower.
Polyhydric alcohols of which two hydroxyl groups have a primary structure are preferred from the standpoint of rapid depolymerization. Such polyhydric alcohols include neopentyl glycol, 2-methyl-1,3-propanediol, and 3-methyl-1,5pentanediol. The polyhydric alcohol for PET depolymerization is selected appropriately depending on the molecular design, and the performance required, of the unsaturated polyester. If desired two or more kinds of polyhydric alcohols can be used in combination. A preferred weight ratio of the polyhydric alcohol to PET ranges from 30:37 to 90:10.
The PET depolymerization with the polyhydric alcohol is preferably carried out in a relatively low temperature ranging from 200 to 260xc2x0 C. Desirably, a catalyst is used to accelerate the depolymerization. Suitable catalysts include organic acid salts, alkoxides or chelates of metals. It is desirable to decide the kind and the amount of the catalyst so as not to impair the physical properties of the resin. From this viewpoint, a preferred catalyst is a tin compound, particularly a monobutyltin compound, and a preferred amount of the catalyst is from 0.01 to 1.0% by weight based on the total weight of the polyhydric alcohol and PET.
The resulting PET depolymerization product is a mixture of ethylene terephthalate oligomers having ethylene glycol or the glycol used in step (A) at the end thereof, which further comprises glycol diterephthalate, free glycols, such as the glycol used in step (A) and ethylene glycol, and the like.
After step (A), the PET depolymerization product (mixture) is preferably cooled to 150xc2x0 C. or lower. In step (B), a requisite amount of maleic anhydride is added to the mixture and allowed to react with the depolymerization product. In step (C), DCPD is added to the reaction mixture to undergo addition reaction with a carboxyl group of the maleic anhydride. The order of steps (B) and (C) is not particularly limited. The stage of adding DCPD can be decided according to the production equipment. As far as exotherm is controllable, DCPD may be added either before or after, or simultaneously with the addition of maleic anhydride. In a preferred embodiment, addition of maleic anhydride (step (B)) precedes addition of DCPD (step (C)) from the standpoint of reaction controllability.
Maleic anhydride is preferably added in an amount of 40 to 100% by weight based on the PET depolymerization product.
DCPD is preferably added in an amount of 20 to 50% by weight based on the PET depolymerization product. The addition reaction of DCPD is preferably carried out in a temperature range of from 120 to 150xc2x0 C., in which DCPD is prevented from degradation into cyclopentadiene (CPD), etc., thereby securing a desired structure of the resin. It should be understood that the reaction temperature is by no means limited to the above range. That is, in cases where Diels-Alder reaction of CPD with maleic acid to produce nadic acid (i.e., norbornenedicarboxylic acid) is desired for the performance of the resulting unsaturated polyester resin, the addition reaction of DCPD can be conducted at temperatures exceeding 150xc2x0 C.
In order to achieve the addition reaction of DCPD with the carboxyl group of the maleic acid, setting of the acid value of the final reaction product of step (1) is of importance. Specifically, the theoretical acid value at the time when the added DCPD is 100% added to the maleic acid is calculated from their respective charged amounts, and the thus calculated value is determined as a design acid value. In order to complete the addition of DCPD to the maleic acid smoothly, the design acid value is preferably 100 mgKOH/g or more. More preferably, it is desirable to obtain the reaction product after the completion of step (1) having the acid value of from 140 to 300 mgKOH/g. Further, the molar ratio of dicyclopentadiene in step (C) to maleic anhydride in step (B) of the present invention is preferably from 0.15:1 to 0.5:1.
In the present invention, controlling of the addition rate of DCPD to the carboxyl group of the maleic acid is also of importance. As the method of tracing the addition rate, a method which comprises measuring the acid value of the reaction product in step (C), comparing the value with a design acid value, and examining the reduced amount of the acid value is easy and preferable.
For the purpose of controlling the degree of ring opening of the maleic anhydride and increasing the final theoretical acid value, a polyhydric alcohol or a small amount of water may be added to the reaction system immediately before the ring-opening reaction. If water is added, it is desirable to use water in a molar ratio of water to the maleic anhydride of from 0.01:1 to 0.5:1 from the standpoint of the resin properties. If the water is used within the above range, production of maleic acid diester compounds of DCPD can be inhibited. Further, the production example using this technique falls within the scope of the invention.
Addition reaction of DCPD is conducted until the acid value is reduced to a prescribed level to complete step (C), which means the end of step (1). As described above, the degree of addition of DCPD can be traced by examining the reduced amount of the acid value. A preferred degree of addition reaction is 90 mol % or more.
In step (2) prescribed amounts of a polyhydric alcohol and/or a polybasic acid are added to the reaction mixture. After the reaction atmosphere is sufficiently displaced with an inert gas, such as nitrogen, the temperature is raised to cause dehydration and polycondensation. The reaction is preferably performed at 180 to 220xc2x0 C. until the acid value is reduced to a desired value, particularly 20 to 40 mgKOH/g. There is thus produced an unsaturated polyester.
The polyhydric alcohol which can be used in steps (1) and (2) typically include dihydric alcohols, such as ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2 4-trimethyl-1,3-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, dipropylene glycol, hydrogenated bisphenol A, an alkylene oxide adduct of hydrogenated bisphenol A, hydrogenated hydroquinone, and an alkylene oxide adduct of bisphenol A; and tri functional or more functional polyhydric alcohols, such as glycerol and trimethylolpropane. These polyhydric alcohols can be used either individually or as a combination thereof. The polyhydric alcohols to be used are selected appropriately according to the desired performance. If desired, a monohydric alcohol, such as benzyl alcohol, can be used in combination for viscosity adjustment. In step (2) the polyhydric alcohol is preferably added in an amount of 30% by weight or less based on the reaction product of step (1). A greater amount is sometimes added depending on the prescribed percent excess of polyhydric alcohol.
The polybasic acids which can be used in step (2) typically include unsaturated polybasic acids, such as maleic acid, maleic anhydride, fumaric acid, and itaconic acid; aliphatic saturated polybasic acids, such as malonic acid, succinic acid, adipic acid, azelaic acid, and sebacic acid; aromatic saturated polybasic acids, such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, and 2,6-naphthalenedicarboxylic acid; and alicyclic saturated polybasic acids, such as tetrahydrophthalic anhydride, 1,2-hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, and nadic acid. These polybasic acids can be selected appropriately according to the desired performance either individually or as a combination thereof. The polybasic acid is preferably added in an amount of 30% by weight or less based on the reaction product of step (1). If necessary, monofunctional acids, such as benzoic acid and 4-t-butylbenzoic acid, may be added for viscosity adjustment.
The resulting unsaturated polyester is dissolved in a radical polymerizable unsaturated monomer in a usual manner to provide a liquid unsaturated polyester resin composition. The radical polymerizable unsaturated monomers include, but are not limited to, styrenes, acrylic esters, methacrylic esters, and diallyl phthalate. Suitable unsaturated monomers are selected according to the use and desired performance of the unsaturated polyester resin composition.
According to the process of the invention, an unsaturated polyester with stable performance can always be produced on a large scale without requiring expensive hydroxylated DCPD nor involving a complicated step of adding a separately prepared compound such as a DCPD maleic acid monoester.
The process of producing the unsaturated polyester and the composition thereof according to the present invention can be carried out sufficiently with conventional equipment for unsaturated polyester resin production.
The unsaturated polyester resin composition of the present invention is compounded with a low profile additive, a filler, a reinforcement, a curing agent, a colorant, a release agent, a thickener, and so forth to prepare a molding material (compound). The resin composition and the molding compound according to the invention can be handled in the same manner as for conventional unsaturated polyester resin compositions which are not prepared from PET. The molding compound of the invention exhibits excellent molding properties and stably provides molded articles with high quality and good appearance.
The unsaturated polyester resin composition according to the present invention is also useful as a matrix of fiber-reinforced plastics (FRP) comprising glass fiber (GF) as a main reinforcement. If desired, the resin composition can be mixed with a general unsaturated polyester resin composition or an air-drying unsaturated polyester resin composition to have improved properties or air-drying properties.
If desired, the unsaturated polyester resin composition can contain various additives commonly used in the production of liquid resin compositions, such as a curing agent, a cure accelerator, a polymerization inhibitor, a wax, a thixotropic agent, a reinforcement, a filler, a colorant, and the like.
The molding compound according to the present invention comprises the above-described unsaturated polyester resin composition as a main component and, in addition, a low profile additive, a reinforcement, a filler, a thickener, a curing agent, etc. and includes SMC and BMC. The molding compound can further contain other appropriately selected additives, such as a colorant, a release agent, a viscosity reducing agent, a silane coupling agent, a polymerization inhibitor, and the like.
The low profile additive which can be used in the molding compound includes, but is not limited to, thermoplastic polymers, such as polystyrene, polymethyl methacrylate, polyethylene, polypropylene, saturated polyester, and polyurethane. Three-dimensional crosslinked particles of these polymers are also useful. Suitable low profile additive can be selected according to the use or desired performance of the compound. Usually, polystyrene is frequently used for its water resistance and inexpensiveness. In the practice of unsaturated polyester resin molding materials, how to control the compatibility with polystyrene as a low profile additive is of significance. In this respect, the unsaturated polyester prepared by the process of the present invention exhibits satisfactory performance.
The reinforcement which can be used in the molding compound according to the present invention includes, but is not limited to, glass fiber, carbon fiber, aramid fiber, and mixed fiber thereof. Glass fiber is frequently used for its inexpensiveness.
The filler which can be used in the molding compound includes, but is not limited to, calcium carbonate, aluminum hydroxide, clay, talc, and silica. While a suitable filler is selected according to the use and desired performance of the molding compound, calcium carbonate is usually used for its excellent strength properties and inexpensiveness. The filler may be surface-treated.
The thickener which can be used in the molding compound includes, but is not limited to, polyvalent metal oxides, such as magnesium oxide and calcium oxide; and polyisocyanate compounds, such as crude diphenylmethane diisocyanate. While a suitable thickener can be selected according to the use and desired performance of the molding compound, magnesium oxide is generally used, with which the thickening degree can be controlled easily.
The curing agent which can be used typically includes organic peroxides, such as methyl ethyl ketone peroxide, t-butyl peroxyisopropyl carbonate, and t-butyl peroxybenzoate, and azo compounds, such as azobisisobutyronitrile. In particular, there are many organic peroxide curing agents, from which a suitable compound can be selected depending on the molding temperature and cycle determined based on the molded article productivity.
The colorant can be chosen from various organic or inorganic pigments, such as phthalocyanine compounds and titanium dioxide, and the like according to a desired hue. The pigment is generally added in the form of toner particles comprising an unsaturated polyester resin having the pigment uniformly dispersed therein.
The polymerization inhibitor to be used includes, but is not limited to, hydroquinone, toluhydroquinone, and p-benzoquinone. A suitable polymerization inhibitor is selected according to the molding properties of the molding compound.
The release agent which can be used include, but is not limited to, fatty acids, such as stearic acid and lauric acid, and metal salts thereof, such as zinc or calcium salts. A suitable release agent is selected according to the molding conditions.
Commercially available viscosity modifiers such as a viscosity reducing agent and commercially available silane coupling agents can be made use of.
The unsaturated polyester resin composition of the invention can also be mixed with an aggregate and a filler to provide resin concrete.